U.S. patent number 5,373,851 [Application Number 08/047,495] was granted by the patent office on 1994-12-20 for specialized peak flow meter.
This patent grant is currently assigned to Brunswick Biomedical Corporation, The Johns Hopkins University. Invention is credited to O. Napoleon Monroe, Herbert E. Reinhold, Jr., Martin D. Valentine.
United States Patent |
5,373,851 |
Reinhold, Jr. , et
al. |
December 20, 1994 |
Specialized peak flow meter
Abstract
The present invention provides a peak flow meter which
facilitates a subject's compliance with the use thereof. In one
embodiment, the peak flow meter provides an alarm for indicating
that the subject is due for a peak expiratory flow rate evaluation
when the subject has failed to use the peak flow meter after a
predetermined period of time. In another embodiment, the peak flow
meter is provided with circuitry which derives a data result
corresponding to the peak expiratory flow rate of air blown into
the peak flow meter for a number of blows. A first comparator
determines the best data result within the number of blows and a
memory stores each best data result. A second comparator compares
each best data result to a specified value and provides an enabling
signal to an alarm when a best data result is a predetermined
amount lower than the specified value. To provide an incentive for
the subject to blow as hard as possible into the peak flow meter,
the a comparator may also compare each data result to the previous
data result and provide an indication when the most recent data
result is greater than the preceding data result.
Inventors: |
Reinhold, Jr.; Herbert E.
(Rockville, MD), Valentine; Martin D. (Baltimore, MD),
Monroe; O. Napoleon (Bethesda, MD) |
Assignee: |
Brunswick Biomedical
Corporation (Marlboro, MA)
The Johns Hopkins University (Baltimore, MD)
|
Family
ID: |
21949302 |
Appl.
No.: |
08/047,495 |
Filed: |
April 19, 1993 |
Current U.S.
Class: |
600/529; 482/13;
600/538 |
Current CPC
Class: |
A61B
5/0871 (20130101); A61B 5/411 (20130101) |
Current International
Class: |
A61B
5/08 (20060101); A61B 5/087 (20060101); A61B
005/091 () |
Field of
Search: |
;128/725-730,716
;73/861.71 ;340/611 ;482/13 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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|
|
|
|
1224387 |
|
Mar 1971 |
|
GB |
|
1338501 |
|
Nov 1973 |
|
GB |
|
1500627 |
|
Feb 1978 |
|
GB |
|
1521412 |
|
Aug 1978 |
|
GB |
|
2238130 |
|
May 1991 |
|
GB |
|
2238389 |
|
May 1991 |
|
GB |
|
Primary Examiner: Cohen; Lee S.
Assistant Examiner: Nasser, Jr.; Robert L.
Attorney, Agent or Firm: Cushman Darby & Cushman
Claims
What is claimed is:
1. A peak flow meter comprising:
a conduit through which air can be blown by a subject, said conduit
having a restriction therein for causing air blown into said
conduit to escape said conduit at a restricted rate therefrom and
create a pressure rise therein;
pressure sensing means for generating an electrical signal
corresponding to said pressure rise within said conduit each time
the subject blows into said conduit;
data processing means for processing each said electrical signal
and for deriving data results corresponding to peak expiratory flow
rates of air blown into said conduit for any number of blows by the
subject;
first comparison means having a memory for storing said data
results and comparing said data results to one another for said
number of blows by the subject to derive a best data result
corresponding to a best peak expiratory flow rate attained by the
subject in said number of blows;
second comparison means for comparing said best data result in said
number of blows to a specified value and for generating an output
signal when said best data result is a predetermined amount lower
than said specified value; and
alarm means, responsive to said output signal, for generating an
indication when said best data result is said predetermined amount
lower than said specified value.
2. A peak flow meter as claimed in claim 1, further comprising:
third comparison means for comparing each data result to at least
one preceding data result derived by said data processing means and
for generating a greater indication signal when a most recent data
result is greater than said preceding data result; and
indication means, responsive to said greater indication signal, for
indicating that the most recent data result is greater than said
preceding data results.
3. A peak flow meter as claimed in claim 1 wherein said second
comparison means comprises memory means for storing said specified
value, said specified value being a predetermined reference data
result.
4. A peak flow meter as claimed in claim 1 wherein said first
comparison means expels a data result previously stored therein
when a subsequent data result is greater than said previously
stored data result, said subsequent greater data result being
stored in said first comparison means in place of said previously
stored data result.
5. A peak flow meter as claimed in claim 1 wherein said second
comparison means comprises memory means for storing a plurality of
previously derived best data results, and wherein said specified
value is a variable dependent upon at least one of said previously
derived best data results stored in said memory means.
6. A peak flow meter as claimed in claim 5 wherein said memory
means comprises a means for recording a date and time of each said
best data result stored therein.
7. A peak flow meter as claimed in claim 1 wherein said second
comparison means comprises a rolling memory for storing a
predetermined number of previously derived best data results and
wherein said specified value is a variable dependent upon at least
one of said best data results previously derived and stored in said
rolling memory.
8. A peak flow meter as claimed in claim 1 further comprising means
for measuring a period of time between blows by the subject, and
wherein said number of blows is equivalent to a number of instances
the subject has blown into said conduit when the subject fails to
blow into said conduit after a predetermined period of time.
9. A peak flow meter as claimed in claim 1 wherein said pressure
sensing means, said data processing means, said first comparison
means, said second comparison means and said alarm means are
contained in a housing separable from said conduit.
10. A peak flow meter as claimed in claim 9 wherein said conduit
comprises means for storing said housing when said peak flow meter
is not in use.
11. A peak flow meter as claimed in claim 1 further comprising a
means for transmitting said best data results to a remote
location.
12. A peak flow meter providing a prompt for facilitating a
subject's compliance with the periodic use thereof comprising:
a conduit through which air can be blown by a subject;
means for evaluating a peak expiratory flow rate attained by the
subject when the subject blows into said conduit;
indicating means for indicating that the subject is due for said
peak expiratory flow rate evaluation when the subject fails to blow
into said conduit after a predetermined time period since the
subject's last peak expiratory flow rate evaluation; and
means for discontinuing the indication in response to the subject's
compliance with the use of the peak flow meter by blowing into the
conduit in a manner sufficient to permit the evaluating means to
evaluate the peak expiratory flow rate of the subject.
13. A peak flow meter as claimed in claim 12 further comprising
timing means for measuring said predetermined time period.
14. A peak flow meter as claimed in claim 13, further comprising
means for resetting said timing means so that said predetermined
time period begins to run anew, and wherein said means for
discontinuing said indication and said resetting means are actuated
when the subject blows into said conduit in a manner sufficient to
permit the evaluating means to evaluate the peak expiratory flow
rate of the subject.
15. A peak flow meter as claimed in claim 12 wherein said
indicating means comprises timing means for measuring said
predetermined time period and alarm means generating an alarm when
the subject fails to blow into said conduit after said
predetermined time period.
16. A peak flow meter as claimed in claim 15 wherein said timing
means comprises means for adjusting said predetermined time
period.
17. A peak flow meter as claimed in claim 15 wherein said alarm
means is at least one of a tone generator and a visual display.
18. A peak flow meter comprising:
a conduit through which air can be blown by a subject, said conduit
having a restriction therein for causing air blown into said
conduit to escape at a restricted rate therefrom and create a
pressure rise therein;
pressure sensing means for generating an electrical signal
corresponding to said pressure rise within said conduit each time
the subject blows into said conduit;
data processing means for processing each said electrical signal
and for deriving data results corresponding to peak expiratory flow
rates of air blown into said conduit for any number of blows by the
subject;
comparison means for comparing each data result to at least one
preceding data result derived by said data processing means and for
generating a greater indication signal when a most recent data
result is greater than said preceding data result; and
indication means, responsive to said greater indication signal, for
indicating that the most recent data result is greater than said
preceding data result.
19. A peak flow meter as claimed in claim 18 wherein said
comparison means generates a lower indication signal when the most
recent data result is lower than that of preceding data result,
said indication means responsive to, and capable of differentiating
between, said greater and said lower indication signals for
indicating to the subject whether the most recent data result is
greater or less than said preceding data result.
20. A peak flow meter as claimed in claim 19 wherein said
comparison means further comprises rolling memory means for storing
a predetermined number of said successive data results.
21. A peak flow meter as claimed in claim 20 wherein said
indication means is at least one of a tone generator and a visual
display.
22. A peak flow meter as claimed in claim 18, wherein said
preceding data result compared to said most recent data result by
said comparison means is a data result which immediately precedes
said most recent data result, and wherein said indication means,
responsive to said greater indication signal, indicates when the
most recent data result is greater than said immediately preceding
data result.
23. A peak flow meter comprising:
a conduit having an inlet through which air can be blown by a
subject, said conduit having a restriction therein for causing air
blown into said conduit to escape at a restricted rate therefrom
and create an air pressure rise therein, said conduit including a
flexible element which flexes in response to said pressure rise in
said conduit; and
peak expiratory flow measuring means cooperable with said conduit
for deriving a peak expiratory flow rate of said subject, said peak
expiratory flow measuring means including: i) a pressure transducer
having a chamber defining an inner air space, said pressure
transducer being capable of measuring air pressure within said
chamber and generating a signal based upon said air pressure within
said chamber, and ii) circuitry means responsive to said signal for
deriving said peak expiratory flow rate of said subject;
said peak expiratory flow measuring means being cooperable with
said conduit in a manner such that: i) said peak expiratory flow
measuring means being selectively separated from and reattached to
said conduit so that said conduit is adapted to be sterilized as a
separate unit, ii) said flexible element of said conduit can be
brought into airtight communication with said inner air space
within said chamber to prevent external air from entering said
chamber, and iii) flexing of said flexible element towards said
inner air space of said chamber creates a pressure rise in said
chamber corresponding to the pressure rise in said conduit thereby
enabling said pressure transducer to generate said signal as a
function of the pressure rise within said conduit so that said
circuitry means can derive said peak expiratory flow rate of said
subject through said conduit.
24. A peak flow meter as claimed in claim 23 wherein said flexible
element seals an opening within said conduit.
25. A peak flow meter as claimed in claim 24 wherein said seal is
airtight.
Description
This invention relates to pulmonary function measuring devices and
more particularly to peak flow meters. Peak flow meters are used in
the medical field for the measurement of human respiratory
capabilities and are especially useful for asthma and emphysema
patients. Conventional peak flow meters are capable of achieving
precise measurements of varying parameters defining the subject's
peak expiratory flow rate (PEFR), which is the greatest flow
velocity that can be obtained during forced expiration starting
with fully inflated lungs. A detected decrease in PEFR may signify
the onset of a potentially harmful pulmonary airflow
obstruction.
While peak flow measurements are often performed by medical
personnel using highly sophisticated equipment incorporating, for
example, computer analyses and chart recorders, experts in the
medical field recommend regular home use of peak flow meters for
continuous monitoring and an early detection of a decrease in PEFR.
Such early detection enables a respiratory subject to seek
treatment before respiratory problems worsen. In addition, home
monitoring may help patients determine which specific allergens or
workplace exposures exacerbate their symptoms. Therefore, the
present invention provides an inexpensive, easy to use peak flow
meter which provides accurate readings and is suited for in-home
use.
A primary limitation of the accuracy of peak flow meter monitoring,
however, is that it is effort dependant. Effective respiratory
monitoring depends largely on the patient's willingness to use the
peak flow meter on a regular basis. A typical respiratory patient
is required to monitor PEFR on a regular daily basis, although more
or less frequent measurements may be required depending upon the
particular patient's respiratory condition. Because such frequent
peak flow measurements can become tedious, many patients become lax
in their compliance with using the peak flow meter. Other patients
may simply forget to use the instrument. Therefore, there exists a
need for a peak flow meter which will effectively enhance patient
compliance.
Therefore, it is an object of the present invention to fulfill the
need expressed above. In accordance with the principles of the
present invention, this objective is achieved by providing a peak
flow meter which provides a prompt for facilitating a subject's
compliance with the periodic use thereof. The peak flow meter
includes a conduit through which air can be blown by the subject
and a means for evaluating a peak expiratory flow rate attained by
the subject when the subject blows into the conduit. An indicating
means is provided for indicating that the subject is due for a peak
expiratory flow rate evaluation when the subject fails to blow into
said conduit after a predetermined time period since the subject's
last peak expiratory flow rate evaluation.
The effective use of currently available peak flow meters is also
limited by the fact that they merely provide the patient with a
numerical measurement reading corresponding to the peak expiratory
flow rate. Unless tedious monitoring and recording of data are
performed, the numerical reading is a meaningless number rather
than a clear indication of whether the patient is in need of
medical attention.
Thus, another object of the present invention is to provide a peak
flow meter having an alarm means for providing an indication to the
subject that the measured PEFR is a predetermined amount lower than
a specified value. In this embodiment, the peak flow meter includes
a conduit through which air can be blown by a subject and a
restriction means causing air blown into the conduit to escape at a
restricted rate therefrom and create a pressure rise therein. A
pressure sensing means generates an electrical signal corresponding
to the pressure rise within the conduit, and a data processing
means processes the electrical signal to derive a data result
corresponding to the peak expiratory flow rate of the air blown
into the conduit. A comparison means compares the data result to a
specified value and generates an output signal when the data result
is a predetermined amount lower than the specified value. Finally,
an alarm means, in response to the output signal, indicates when a
data result is a predetermined amount lower than the specified
value.
Since PEFR is the greatest flow velocity that can be obtained
during forced expiration, a subject's failure to exhale with
maximum effort will result in inaccurate PEFR readings. It is
therefore advantageous to take several measurements; the best of
those measurements being used in establishing an accurate PEFR
result. Thus, in another embodiment, there is provided a peak flow
meter having a conduit through which air can be blown by a subject
and a restriction means causing air blown into the conduit to
escape at a restricted rate therefrom and create a pressure rise
therein. A pressure sensing means generates an electrical signal
corresponding to the pressure rise within the conduit each time the
subject blows into the conduit. A data processing means processes
each electrical signal to derive data results corresponding the
peak expiratory flow rates of air blown into the conduit for a
number of blows by the subject. A first comparison means compares
data results to one another for the number of blows by the subject
and derives a best data result among them. This best data result
corresponds to a best peak expiratory flow rate attained by the
subject in the number of blows. Next, a second comparison means
generates an output signal if the best data result is a
predetermined amount lower than a specified value. Finally, an
alarm means, in response to the output signal, generates an
indication if the best data result is a predetermined amount lower
than the specified value.
It is also advantageous to further provide a means of inducing the
subject to exhale with maximum effort in order to obtain an
accurate best PEFR result within the a set of PEFR measurements.
Such inducement can be accomplished by providing a peak flow meter
having a conduit through which air can be blown by a subject and a
restricting means for causing air blown into the conduit to escape
at a restricted rate therefrom and create a pressure rise therein.
A pressure sensing means generates an electrical signal
corresponding to the pressure rise within the conduit each time the
subject blows into the conduit. A data processing means processes
each electrical signal and derives data results corresponding to
the peak expiratory flow rates of air blown into the conduit for a
number of blows by the subject. A comparison means compares
successive data results derived by the data processing means and
generates a greater indication signal when a most recent data
result is greater than a preceding data result. Finally, an
indication means, responsive to the greater indication signal,
provides an indication to the subject when the most recent data
result is greater than the preceding data result. This provides a
respiratory patient a goal or incentive to exceed the preceding
PEFR measurement so that a truly best PEFR measurement is
attained.
Another object of the present invention addresses the problem of
cross-contamination of peak flow meters between patients. Peak flow
meters are difficult to sterilize because they contain electronic
and/or moving parts which are easily damaged. While most peak flow
meters provide a removable mouthpiece which can be separately
sterilized, the electronic or moving components remain contaminated
by human expiration and may become a potential source of
disease.
The present invention resolves the aforementioned problem by
providing a means of measuring the peak expiratory flow rate of the
subject without exposing the electrical components of the pressure
transducer directly to human expiration. A flexible element is
provided in air communication with the conduit of a peak flow meter
which flexes in response to a pressure rise in the conduit. A
chamber portion of the pressure transducer has an inner space,
which is in airtight communication with the flexible element.
Flexing of the flexible element towards the inner air space creates
a pressure rise in the chamber corresponding to a pressure rise
generated in the conduit when a subject blows therein. The pressure
transducer is thus able to provide a pressure measurement
corresponding to the pressure within the conduit without direct
exposure to the air blown therein.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a longitudinal sectional view of the peak flow meter
embodying the principles of the present invention;
FIG. 2 is a perspective view of a peak flow meter embodying the
principles of the present invention;
FIG. 3 is a longitudinal sectional view of a disassembled peak flow
meter embodying the principles of the present invention;
FIG. 4A is a block diagram showing an arrangement of a peak flow
meter embodying the principles of the present invention;
FIG. 4B is a block diagram showing an arrangement of a peak flow
meter embodying the principles of the present invention;
FIG. 5 is a block diagram showing an arrangement of a peak flow
meter embodying the principles of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
Referring, more particularly, to the drawings, there is shown in
FIG. 1 thereof a peak flow meter, generally indicated at 10, which
embodies the principles of the present invention. The peak flow
meter includes two basic assemblies: (1) a conduit, indicated at
12; and (2) an electronic housing, indicated at 14. Conduit 12 has
an orifice 16, seen more clearly in FIG. 3, in which conduit 12 and
electronic housing 14 are disassembled and flexible element 66 has
been removed.
Referring back to FIG. 1, it can be appreciated that conduit 12 is
mounted on the electronic housing 14. The electronic housing 14
carries peak expiratory flow measuring means including a pressure
transducer 22 and circuitry means cooperable with the transducer to
derive the peak expiratory flow rate of a subject. It can be
appreciated that pressure transducer 22 includes a chamber 20, a
chamber opening 18, an inner air space 28, a diaphragm 30, and
electronic circuitry, not shown in the figures, which generates
electrical signals in response to flexing of diaphragm 30. Chamber
opening 18 securely fits into orifice 16 of conduit 12 to form an
airtight seal with the edge wall 17, seen more clearly in FIG. 3,
surrounding orifice 16. The airtight seal between the edge wall 17
surrounding orifice 16 and chamber opening 18 may be formed merely
by a close tolerance between the diameter of orifice 16 and the
outer diameter of chamber opening 18. Alternatively, the seal may
be in the form of a fitted connection such as a threaded
connection, or in some other form.
When a subject places his or her lips around inlet 34 at one end of
conduit 12 and blows, a pressure rise is created within conduit 12.
To enhance the pressure rise, a restriction 32 is placed in the
conduit at the end opposite inlet 34. Restriction 32 is, in the
most preferred embodiment, a sudden narrowing in the air passage of
conduit 12 as shown in FIG. 1. While restriction 32 need not be
positioned at the furthest extremity from inlet 34 of conduit 12,
as in FIG. 3, it must be positioned such that orifice 16 is
disposed between inlet 34 and restriction 32 so that pressure
transducer 22 receives the full effect of the pressure rise. In
response to the pressure rise in conduit 12, diaphragm 30 of
pressure transducer 22 acts as a pressure sensor and causes
pressure transducer 22 to generate an electrical signal
corresponding to the magnitude of the pressure rise.
The conduit 12 may be provided with flexible element 66 which
sealingly covers orifice 16. The purpose of flexible element 66 is
to prevent moisture and germ contamination from entering chamber 20
of pressure transducer 22. If moisture and/or mucus are permitted
to enter chamber 20, germs and bacteria may begin to inhabit
chamber 20 and become a source of disease. By sealing orifice 16
with flexible element 66, human expiration is prevented from
entering chamber and, as a result, chamber 20 is kept sterile.
Since conduit 12 can be separated from electronic housing 14 and
contains no electronic circuitry, it can be effectively
sterilized.
Although flexible element 66 prevents human expiration from
entering chamber 20, an accurate pressure reading of air blown into
the chamber can nevertheless be obtained. When flexible element 66
is in place, it will flex towards inner space 28 of chamber 20 in
response to a pressure rise in conduit 12. Since the inner air
space 28 of chamber 20 is in airtight communication with flexible
element 66, such flexing towards said inner air space 28 of chamber
20 creates a pressure rise in chamber 20 which is substantially
proportional to the pressure rise in conduit 12. Pressure
transducer 22 is calibrated accordingly to generate an electrical
signal which can be converted into a digital reading indicative of
the peak expiratory flow rate of the subject.
It can be appreciated that flexible element 66, in the broader
aspect of the invention, need not be sealed to orifice 16. Flexible
element 66 may, instead, be sealed to chamber opening 18 and still
have the same pressure transmitting effects into chamber 20.
Alternatively, flexible element 66 need not be sealed to either
orifice 16 or chamber opening 18, but merely sandwiched between the
outer diameter of chamber opening 18 and the surrounding edge wall
17 of orifice 16.
Referring now to FIG. 2, it can be seen that the peak flow meter is
provided with an LED display 31. This display provides PEFR
measurements to the subject. The display may also provide warning
indications in accordance with some of the following
embodiments.
Referring now to FIG. 3, the peak flow meter is shown in its
disassembled storage condition. Since a further limitation to the
regular use of peak flow meters stems from the fact that many of
the commercial devices are bulky and do not lend themselves to
being carried by the patient, a further object of the present
invention is to provide a peak flow meter which is compact in its
storage condition. Therefore, the peak flow meter of the present
invention is disassembleable into two separate components, one of
which is capable of receiving the other when the peak flow meter is
not in use, thereby forming a compact, easily transportable device.
To provide this smaller storage package, the inner space 19 of
conduit 12 is large enough to receive the electronic housing 14. A
clip member 13 is fixed to the exterior of conduit 12 to enable the
peak flow meter to be secured to a shirt pocket or the like when
the peak flow meter is not in use.
Referring now to FIG. 4A, the peak flow meter is provided with
circuitry for comparing measured PEFR results with a specified
value. The circuitry includes pressure sensor 80 which detects a
pressure rise within the conduit of a peak flow meter and generates
an electrical signal corresponding to the magnitude of the pressure
rise. Data processor 82, in response to the electrical signal,
converts the analogue signal into a digital measurement or data
result. Comparator 84 compares this data result with a specified
value stored in storage element 86. The specified value may, for
example, be a fixed reference data result corresponding to a
predetermined fixed peak expiratory flow rate, such as a peak
expiratory flow rate established when the patient is healthy.
Alternatively, the specified value may be a variable dependant upon
one or more data results previously derived by data processor 82.
For example, such variable may be an average of a predetermined
number of previously attained peak expiratory flow rates or may be
simply equivalent to the previously attained peak expiratory flow
rate.
When comparator 84 determines that a data result is a predetermined
amount lower than the specified value, alarm 88 is enabled and
provides an indication to the subject that immediate medical
attention may be required. It is appreciated that the
aforementioned predetermined amount may be equivalent to zero, so
that alarm 88 is enabled whenever a data result is below the
specified value.
Alarm 88 may comprise an audio and/or visual indicator. A display
90 may also be included to provide a visual read-out of data
results.
Referring now to FIG. 4B, a flow diagram is shown generally at 40
representing the logical electrical processing circuitry of another
embodiment of the present invention.
Since PEFR is the greatest flow velocity that can be obtained
during forced expiration, it is advantageous to take several
measurements in establishing an accurate PEFR evaluation. Thus, in
this embodiment, before comparing an established peak expiratory
flow rate to either a fixed or variable specified value, a set of
several measurements may be taken, the best of which is then
compared.
In this embodiment, pressure sensor 42 detects a pressure rise
within the conduit of a peak flow meter, such as conduit 12 shown
in FIG. 1, when a subject blows therein. Pressure sensor 42
generates an electrical signal corresponding to the magnitude of
the pressure rise.
Data processor 44, in response to the electrical signal generated
by pressure sensor 42, converts the analogue signal into a useful
digital measurement or data result.
A first comparison is accomplished by first comparator 50 and
storage element 48 in order to obtain a best data result
corresponding to the best PEFR attained within a set of PEFR
measurements. To accomplish this, data processor 44 provides its
digital output to first comparator 50, which compares each data
result to the preceding data result, which has been previously
stored in storage element 48. If the data result is the first data
result received by the peak flow meter within a set of blows, it
will be stored by storage element 48 without such comparison. After
performing each comparison, first comparator 50 sends the greater
of the two data results back into storage element 48 until the next
data result is received. The output of first comparator 50 also
sends the greater of the two data results to display 46, typically
an LED (light emitting diode) display, which displays the
prevailing data result within the present set of blows. After a set
of data results has been completed, an ultimately prevailing best
data result is achieved. In the broadest aspects of the present
invention, it is appreciated that storage element 48 may store all
data results within a given set, and comparator 50 may then
undertake one comparison of all data results stored in storage
element 48 in determining the best data result among them.
The number of data results constituting a set for which data
results will be compared may either be a predetermined fixed number
or a varying number. In the most preferred embodiment, the number
of data results which will be compared is equal to the number of
times the subject blows into the conduit before the subject finally
fails to blow into the conduit within a predetermined period of
time. For example, if the predetermined period of time is one
minute, storage element 48 will continue to accept data readings to
be compared so long as the subject continues to blow into conduit
12 within one minute after previously blowing into the conduit.
Once one minute elapses without the subject blowing into the
conduit, a best data result is derived for that set of blows.
A timer 60, comprising measurement timer 61, is provided to time
the interval between each blow. In the most preferred embodiment,
measurement timer 61 receives the signal generated by data
processor 44 each time the subject blows into conduit 12. This
signal resets the predetermined time period so that the period
begins to run anew each time the subject blows into the conduit.
When the predetermined time period is finally allowed to lapse,
measurement timer 61 generates an enabling signal to storage
element 48, indicating to storage element 48 that the data result
stored therein is a best data result.
After each best data result is determined, it is then sent to a
memory element. In the most preferred embodiment, the memory
element is a rolling memory, indicated at 52. Rolling memory 52
stores a predetermined number, typically 5 to 10, of the most
recent best data results and expels older best data results.
Each best data result is also sent to second comparator 54, which
then determines when a best data result is a predetermined amount
lower than a specified value. The specified value may be a variable
dependant upon previously attained best data results. In a
preferred embodiment, the specified value is an average of previous
best data results stored in rolling memory 52. Alternatively,
second comparator 54 may compare each best data result to only the
preceding best data result stored in rolling memory 52. As a third
alternative, each best data result determined by first comparator
50 may be compared, in second comparator 54, to one or more
reference data results stored in reference storage element 56. It
is appreciated that second comparator 54 may compare each best data
result to any one, or any combination, of the three aforementioned
alternatives. Then, when second comparator 54 determines that a
best data result is a predetermined amount below the specified
value, alarm 58 is enabled. It is appreciated that the
aforementioned predetermined amount may equal zero.
In the broadest aspects of the present invention, more than one
reference data result may be provided in reference storage element
56. For example, one reference data result may correspond to a peak
expiratory flow rate which indicates that the subject's respiratory
condition is just slightly below normal. When any best data result
is lower than this reference data result, second comparator 54
generates a signal to alarm 58 which provides an indication (i.e.,
a single audio "beep") that the subject is in such condition so
that the appropriate action can be taken (i.e., use an asthma
inhaler). A second reference data result may then also be provided
in reference storage element 56 to indicate, for example, a more
serious respiratory condition. Second comparator 54, indicating
this more serious condition when a best data result is below this
second reference data result generates an appropriate signal to
alarm 58, which then provides an indication distinguishable from
the indication generated at the less serious condition (i.e., two
audio "beeps"). Alarm 58 may provide any type of alerting
indication, such as an audio alarm, an LED indication, a color
light display, or any combination thereof.
Timer 60 also comprises a compliance timer 63, which provides an
enabling signal to alarm 58 if the subject does not blow into
conduit 12 after a predetermined time period since the subject last
blew into conduit 12. The enabling signal generated by compliance
timer 63 enables alarm 58 to provide the respiratory patient an
indication that he or she is due for a peak expiratory flow rate
evaluation and should blow into conduit 12. The typical
predetermined time period is on the order of 24 hours, but that
period may change significantly according to the severity of the
patient's condition. Thus, compliance timer 63 can be adjusted to
set the predetermined time period.
Alarm 58 may incorporate an audio and/or visual indication which is
enabled if the patient fails to undergo a peak expiratory flow rate
evaluation within a predetermined time period since the patient's
last peak expiratory flow rate evaluation. Such an alarm may be
provided in conjunction with any type of peak flow meter,
regardless of the manner in which the flow meter accomplishes its
function (i.e., mechanically or electrically).
Each time a subject blows into conduit 12, the signal generated by
data processor 44 automatically resets compliance timer 63. As a
result, alarm 58 will not be enabled if the subject blows into
conduit 12 before the predetermined time period expires, and only
after compliance timer 63 is allowed to reach the predetermined
time period will alarm 58 be enabled. Therefore, so long as a
subject continues to comply with the regular use of the peak flow
meter by blowing into conduit 12 at regularly spaced time intervals
which are less than the predetermined time period, compliance timer
63 will not generate an enabling signal to alarm 58.
If the predetermined time period should lapse, thereby causing
alarm 58 to be enabled, the subject can disable alarm 58 by simply
blowing into conduit 12. This is accomplished as the electrical
signal generated by data processor 44 also serves to disable alarm
58. In the broader aspects of the present invention, other means of
disabling alarm 58 can be provided, such as a manual switching
mechanism. The same type of switching mechanism can also be used to
manually reset compliance timer 63 if desired. Such a manual reset
can be in place of the above described automatic reset of
compliance timer 63 or can be provided in addition thereto.
Furthermore, in the broader aspects of the present invention, it is
appreciated that when provided with the automatic reset, compliance
timer 63 may receive a resetting signal directly from pressure
sensor 42 rather than from data processor 44.
The peak flow meter may also include a means for communicating best
data results to a remote location. Preferably, the best data
results are transmitted over a telephone line where they are
received by medical personnel who can assess the data. However, the
data results may be transmitted to any external receiver. To
accomplish this, a transmitting device 64 receives best data
results from storage element 48 and is capable of transmitting
digital data over a communication line when a receiver is available
on the other end. Typically, an RS-232 chip, such as the MAX233A
device manufactured by Maxim Integrated Products, is used for
accomplishing this function.
In the broader aspects of the present invention, it is appreciated
that several permutations of the inter-relation between pressure
sensor 42, data processor 44, first comparator 50, storage element
48, display 46, rolling memory 52, second comparator 54, storage
element 56, alarm 58, and timer 60 are possible in accomplishing
the same result.
Referring now to the peak flow meter embodied in FIG. 5, an
incentive is provided to induce the subject to exceed the preceding
PEFR result within a set of PEFR measurements.
In this embodiment, pressure sensor 72 detects a pressure rise
within the conduit of a peak flow meter, such as conduit 12 shown
in FIG. 1, when a subject blows therein. Pressure sensor 72
generates an electrical signal corresponding to the magnitude of
the pressure rise.
Data processor 74, in response to the electrical signal generated
by pressure sensor 42, converts the analogue signal into a useful
digital measurement or data result. A comparator 68 is provided for
comparing successive data results stored in rolling memory 70.
Comparator 68 generates a greater indication signal when the most
recent data result is greater than a preceding data result. Alarm
76, in response to a greater indication signal, generates an
indication that the most recent data result is greater than the
aforementioned preceding data result. Alarm 76 may comprise a
visual display, a tone generator, or a combination thereof.
Comparator 68 may also be capable of generating a lower indication
signal when the most recent data result is lower than that of a
preceding data result. Alarm 76 is responsive to and capable of
differentiating between the greater indication signal and the lower
indication signal for indicating to the subject whether a most
recent data result is greater or less than the preceding data
result in question.
It will be realized that the foregoing preferred specific
embodiments have been shown and described for the purpose of this
invention and are subject to change without departure from such
principles. The invention includes all modifications encompassed
within the spirit and scope of the following claims.
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